‘Martha Dempster is long since dead,’ Raven retorted. ‘You murdered her, along with her parents and her husband-to-be. You are discovered, Mary.’

He saw the briefest flicker of fear in her face at the use of her real name, before the mask came down again.

She was still insisting she was Martha Dempster as McLevy hauled her to her feet and bundled her towards the door.

Simpson appeared momentarily, and with him Findlay. The latter echoed McLevy’s query.

‘Who restrained her?’

‘I thought him a demon, but he was my saviour,’ said Sarah. ‘He hauled her off me and tied her up.’

Simpson looked quizzically to Raven for an explanation.

Raven kept his voice low, mindful that McLevy might still be in earshot.

‘I have friends in low places,’ he said.

Raven put a hand to Sarah’s forehead, feeling for fever and checking her pupils. All seemed normal, but that had been true of the other victims too.

‘What did she give you? Did you drink it?’

‘I don’t know,’ she said weakly. ‘I drank but I thought it was water. It tasted of nothing.’

Sarah pointed to a bag sitting on the sideboard. ‘That is hers,’ she said.

Simpson opened it and began looking inside.

‘I think that she combines atropine with morphine,’ Sarah told them. ‘That is how she disguised her hand. Each compensates for the signs and symptoms of the other.’

‘How fiendishly clever,’ said Simpson. ‘Or cleverly fiendish. But it appears she has given you neither. There are vials here but they are mostly full.’

Raven knew Mary might have believed Sarah did not need her help in dying. He had confessed his fears to that effect to the professor on the ride here. Perhaps as a result of this she had been tentative in her dosing or had been interrupted before she could administer the lethal draught.

‘Let me examine you,’ Simpson said.

While the professor pulled away the bedclothes to look at the wound, Sarah gazed at Raven, her eyes filling. She said but one word.

‘Archie.’

Raven nodded solemnly. ‘He went peacefully, without pain.’

There remained an expectant look in her eyes. He understood what else she still wished to know.

‘And without learning about his child.’

Sarah closed her eyes, the tears spilling down her cheeks, but Raven could tell she had found solace in what he had told her. She reached out her hand and fastened it about his.

‘I owe you my life.’

‘By my accounting that would make us even,’ he told her, though he still feared she might have thanked him too soon.

Simpson looked carefully at the line of stitching, a frown upon his lips. As Raven had warned, there was no pus to be seen, and Simpson appeared perplexed by it, which Raven took to be a bad sign. He was wrong, though.